1. Field of the Invention
The present invention relates to a positive resist developer and a method of developing a positive resist.
2. Description of the Prior Art
Recent advantages in the electronic industries have greatly improved the packing density and micropatterning precision of semiconductor devices. Along with these advances, positive resist materials have been mainly used rather than negative resist materials as materials used for processing semiconductor devices since positive resists have higher resolution than negative resists.
When a positive resist is irradiated with an energy beam such as light, an exposed portion is decomposed and can be removed with a developing solution. Most commercially available positive resist materials are prepared by mixing a photosensitive agent such as o-quinoediazide in cresol-novolak resin. This resist produces a carboxylic group and becomes soluble in alkalis upon radiation of light. A developer for this resist is mainly an organic alkali solution mainly containing a quaternary ammonium salt such as tetramethylammonium hydroxide or trimethylhydroxyethylammonium hydroxide.
However, when the positive resist is developed by using the developer described above, a difference between dissolution rates of an exposed portion of the resist and that of a nonexposed portion thereof is not sufficiently large, thus presenting various problems. In particular, when a resist micropattern having a line width of 1.5 .mu.m or less is developed, a resist foot portion often remains trailed around a boundary between a resist-supporting surface and an edge of the pattern obtained by development. In order to remove such a trailing foot portion by increasing an alkali concentration of the developer, by rising a developing temperature, or by prolonging a developing time, the nonexposed portion is excessively dissolved and the pattern edges are rounded, thereby degrading the pattern precision.